| Under the influence of the drastic change of global climate and the great increase of human social and economic activities,the phenomenon of shortage of water resources and extreme hydrological events occur more and more frequently in the world,which has become one of the major environmental problems facing human society.Scientific understanding of the impact of climate change and human activities on runoff,to correctly identify the changes of hydrological processes and their response mechanisms,as well as to the future runoff response to climate change and human activities make positive anticipation has great help,to guide the rational development and utilization of river basin water and soil resources and the social economic development is of great significance.Located in the northwest of hunan province,Lishui is the smallest branch of the four major rivers of dongting lake.It is one of the three areas with heavy rain in hunan province,which causes frequent floods in the lower reaches of the basin.Based on existing research,this paper taking Lishui basin above shek mun station area as the research object,the systematic analysis of Lishui basin of long series hydrological and meteorological elements space-time evolution characteristics,build a distributed hydrological model basin,the hydrological simulation method and double mass curve method quantitative estimates from different angles,the contribution rate of human activities and climate change on runoff changes,analyses the climate change and human activities in the basin runoff response characteristics,and build the future land use scenario simulation evaluation of land use/cover change of hydrological response process.Through this research,it is expected to provide reference for rational development planning of land use and scientific management of water resources in Lishui basin.Main research contents and achievements are as follows:1.The spatial and temporal distribution of precipitation in Lishui basin is uneven.The precipitation is mainly concentrated in May to August,and the spatial trend from northwest to southeast gradually decreases.The average annual precipitation in the basin is between 1300mm-1900mm.The precipitation in the northwest mountainous area is relatively high,with the annual precipitation reaching more than 1800mm.The precipitation in the southeastern plain region and southwest region is lower than 1500mm.The precipitation in the basin from may to August accounts for about 60%of the total annual value,while the precipitation in the dry season(from December to February)is less than 10%of the annual precipitation.The average annual temperature in Lishui basin is on the rise,and the annual temperature and the temperature in dry season are more obvious than that in flood season.The annual average temperature rise range is 0.15?/10a,the average temperature rise in dry season is more than 0.2?/10a,while the average temperature rise range in flood season is less than 0.02?/10a.The annual temperature of the basin changed suddenly in 1997,and the dry season temperature changed suddenly in 1991 and 2004.2.The annual precipitation,precipitation in flood season and precipitation in dry season are not obvious in the li river basin and its sub-basins.River basin and the two child(Lou water in a river basin and Xie water drainage basins)of annual precipitation and flood season precipitation years performance is not significantly reduced,and the mutagenicity precipitation showed the opposite trend was not significant.The sudden changes in annual precipitation and precipitation in flood season occurred in all three basins in 2005,while the sudden changes in precipitation in dry season occurred in 2010.The annual runoff and flood season runoff show an insignificant trend of decline,while the runoff in dry season shows an obvious trend of rise,and the variation trend of runoff is consistent with that of precipitation.Based on the abrupt change years of the runoff at Shimen station,Changtanhe station and Zaoshi station in different periods,the cut-off point of the hydrological sequence was determined,and the baseline period was 1967-1997,the variation period I from 1998-2006 and the variation period ? from 2007-2016.3.SWAT model has good adaptability in the Lishui basin and can be used to quantitatively study the impact of climate change and human activities on the runoff process.Meteorological and hydrological data using watershed spatial data and establish the whole basin,Lou SWAT model of water basin and Xie basin,on the basis of existing research,choose multisite method of multivariate model parameter calibration,hierarchical watershed SWAT model parameters,and the runoff process simulation,simulation effect is good.4.The contribution rate of climate change and human activities to runoff change is basically the same,but climate change has a greater impact in most of the time,and precipitation reduction is the main factor of runoff reduction in the li river basin.SWAT model based on the basin,the variation of phase I and phase II of the natural runoff variation simulated reduction,distinguish the impact of climate change and human activities on runoff contribution rate,with double mass curve analysis method from the Angle of mathematical statistics,Lishui basin runoff response to climate change and human activities,each factor of runoff showed different degrees of influence.5.The main land use types in Lishui basin are forest,grassland and arable land.From 2000 to 2010,the change of land use/cover in the basin was not obvious,the total area of forest increased by 69.09km2,while the area of cultivated land and grassland decreased by 64.38km2 and 76.94km2 respectively.During the study period,the major land use change in the Lishui basin is the transformation from arable land and grassland to forest land.The increase of forest land can significantly reduce the surface runoff of the basin and increase the evapotranspiration of the basin,thus reducing the total runoff of the basin.Under the natural growth scenario(S1),the urbanization process of the 85th subbasin was very obvious,and the annual surface runoff increased by 47.16%.It can be seen that due to the acceleration of urbanization,the expansion of urban land leads to the increase of impermeable layer area and the decrease of evapotranspiration in the river basin,which leads to the increase of surface runoff.For the scenario of returning farmland to forest(S2),compared with the land use status of the natural growth scenario(S1),both surface runoff and total runoff in the basin decreased.Since the overall change of the area of the scenario constructed in this paper is not significant,the runoff reduction is not obvious,but to a certain extent,it can be seen that ecological restoration measures such as the conversion of farmland to forest have a positive effect on the reduction of runoff. |
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